Why at this point in Bibical progression are there plants?

¹¹ Then God said, “Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, according to their various kinds.” And it was so. ¹² The land produced vegetation: plants bearing seed according to their kinds and trees bearing fruit with seed in it according to their kinds. And God saw that it was good. ¹³ And there was evening, and there was morning—the third day.

This is an easy one. What would first consumer light, air, water and warmth in a cycle of life that is sustainable?

Photosynthesis. The By-Product and that is a very important word of plant consumption is oxygen. Among other things, but, if Earth was first lush and green it was due to the consumption of the elements. 

In any conservation measurement of a system's carrying capacity is the understanding there are primary consumers that also have bi-products that are then considered Primary Producers.

December 15, 2013
Organisms (click here) that use inorganic sources of energy, and particularly plants are the base unit of stored energy in any ecosystem. Light energy is converted to chemical energy by photosynthesis within the cells of plants....

There are also ocean and water plants. They are also primary consumers and their by-products are considered Primary Producers.

There are many scientific theories that follow the path laid out in Genesis. They are variations of the story of Genesis, but, they do not insult the sheer understanding laid down in Genesis.

Are plants vital to Earth's Carrying Capacity? Are you joking? Try living without them. It is not a healthy person or even one that is alive without plants on Earth. Plants are among the first aspects of any ecosystem to adapt and/or mutate.

In the Carrying Capacity of Earth the most important layer of understanding is the amount of plant photosynthesis occurring at any point in time. Photosynthesis is where carbon dioxide is utilized. It seems to that putting plants first is vital to Earth's benevolence. It is benevolence that is the nature of God, is it not? Ultimately, in Genesis it is the benevolent outcome to the creation that comes across as the most important act of God's mind. The creator created. He not only created, he presented it as a gift to the potential of his likeness being benevolent.

So, in understanding Earth's Carrying Capacity there has to be a clear understanding there is a maximum for everything. A maximum for sunlight, heat, atmospheres, oceans and water, water vapor and clouds and rain and plants. 

They are all consumers. But, as we progress through this mindfulness of Earth's elements we are seeing by-products from the consumption and those by-products are considered production. Why? Because with elements being changed in the consumption of biotic systems of Earth, it gives rise to OPPORTUNITY for new biotic content, new life and new consumers.

Earth's elements from the very beginning are opportunities for life.